This invention relates to bypass pressure relief valves and in particular to relief valves finding application in exhaust systems for internal combustion engines. While the invention is described in particular detail with respect to such systems, those skilled in the art will recognize the wider applicability of the inventive concept disclosed hereinafter.
A number of approaches for reducing pollution of the atmosphere caused by automobile internal combustion engines recently have been investigated. One system apparently finding favor injects air obtained from an air pump, which commonly is driven by the crankshaft of the internal combustion engine, into the exhaust system of the engine. Air injected in the exhaust system aids further combustion of the gases expelled from the exhaust valves of the engine, providing additional burning before expulsion of the exhaust gases to the atmosphere. Further reduction of air pollutants expelled by the engine can be obtained by cycling the exhaust gases through a catalytic converter.
The systems utilizing air pumps to support further combustion in the exhaust system in conjunction with catalytic converters present certain difficulties heretofore unresolved in the art. For example, the converters are relatively expensive and can be damaged by excessive heat in the exhaust gases. Consequently, some means for reliably protecting the catalytic converter while simultaneously permitting combustion of the exhaust gases is necessary or various malfunctions to one or more vehicle components may cause damage to otherwise unrelated components of the exhaust system. The catalytic converter especially is sensitive to heat damage which may result if excessive air is inserted into the exhaust system during certain operating periods of the vehicle.
Diaphragm actuated bypass and relief valves are known in the art. For example, the U.S. Patent to Crawford et al, U.S. Pat. No. 3,520,320, issued July 14, 1970, describes one such valve. Fail safe devices also are known in the art. For example, the copending U.S. patent applicationto Crawford, Ser. No. 535,957, filed Dec. 23, 1974 discloses one particular bypass valve form incorporating fail safe features.
In general, prior art valves are intended to function with an air pump commonly driven by the crankshaft of the internal combustion engine by a belt or other mechanical interconnection. The valve is positioned in a line connected between the air pump and the exhaust system. Means are provided for sensing engine manifold vacuum pressure and for controlling main air input to the exhaust system based on manifold pressure. Most air pumps used for this purpose are a positive displacement type. Being positive displacement types, air pump output increases with engine speed. This higher air output generally is not required for proper combustion of the exhaust gases in the exhaust system. The prior art devices indicated above include devices that regulate the air input to the exhaust system by limiting movement of the main valve member to a predetermined distance so that the opened position of the main valve member corresponds to a known input air valve. Excess air is vented to the atmosphere through a pressure relief valve. While these prior art devices worked well for their intended purposes, damage to catalytic converters caused by excessive heat also can result merely by prolonged high speed operation of the vehicle, in the absence of other factors.
My invention prevents damage to the catalytic converter even during prolonged high speed operation, for example, by providing means for closing the main air valve member controlling air input to the exhaust system which operates whenever the pressure relief valve member is actuated. This construction also reduces cost of the valve because using the bypassed air as an aid in closing the main valve lowers the biasing requirement provided by the main valve member spring. Consequently, lower cost spring constructions compatible with the valve of this invention cannot be used with prior art valve designs.
One of the objects of this invention is to provide a bypass pressure relief valve for an internal combustion engine having fail safe features upon loss of engine manifold pressure.
Another object of this invention is to provide a bypass and relief valve incorporating means for closing the main diaphragm actuated valve member under certain predetermined conditions of high air supply.
Another object of this invention is to provide a valve having two operational valve members and dual means for closing one of the operational valve members, all operated in conjunction with a single valve stem.
Other objects of this invention will become apparent to those skilled in the art in light of the following description and accompanying drawing.